The kingdom has tightened controls along its frontier with Syria in recent years and its armed forces occasionally announce operations to foil drug and weapon smuggling attempts from its war-torn neighbour.

"Jordanian warplanes carried out air strikes targeting residential areas and a warehouse in southeastern province of Sweida, killing at least nine people, including two girls and four women," said the Syrian Observatory for Human Rights monitor, describing it as a "massacre".

The first strike on a house in the village of Urman killed a man, his wife and their two daughters, along with his brother and his wife, said the Britain-based group.

The bodies of a man, his mother and aunt were found at the second house that was targeted, added the Observatory, which relies on a network of sources on the ground in Syria for its reports.

The Suwayda24 news website reported that air strikes "likely to have been carried out by the Jordanian air force" killed at least 10 people in Urman.

Observatory director Rami Abdel Rahman said Jordan's armed forces often carry out deadly strikes on civilian homes "on the pretext of fighting drug trafficking".

On this occasion, he said, it remained unclear if the two men targeted in the latest strikes were drug-traffickers.

Rayan Maarouf of Suwayda24, an outlet run by citizen journalists, said however that the men who were killed, along with family members, were believed to have been drug-traffickers.

On January 5, Jordan's official Al Mamlaka television station said the country's air force had carried out two raids in Syria "as part of the pursuit of drug-traffickers".

Jordan was reportedly behind air strikes in Syria on December 18 that killed five people, including a woman and two children.

One of the main drugs smuggled out of Syria is the amphetamine-like stimulant captagon, for which there is huge demand in the oil-rich Gulf.